Some back ground info: Typicaly used in the Hawaiian islands.It is an informal good bye amongst the youth of the islands, but not limited to the use of youngsters. There are some reported cases of use on "The Mainland". When said in a passive manner, one usually throw up a shaka then says the words "Shoots Brah."
A word of many meanings. With a change of tone the words meaning can change instantly. It can be used as a casual good bye^. The word can be used as an aggressive response to a call out also*.
^ First Ex.
Man1: I see you at the party tonight then?
Man2: Yup, just remember to bring the Hards and I'll bring the Budz
Man1: To night is going to be Action, oh shit gotta go.